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Use the Data Booklet to help you answer this question - AQA - A-Level Chemistry - Question 6 - 2017 - Paper 2
Question 6
Use the Data Booklet to help you answer this question. This question is about amino acids and peptide (amide) links. 0 6 . 1 Draw the structure of the zwitterion fo... show full transcript
Worked Solution & Example Answer:Use the Data Booklet to help you answer this question - AQA - A-Level Chemistry - Question 6 - 2017 - Paper 2
Step 1
Draw the structure of the zwitterion formed by phenylalanine.
Answer
The zwitterion of phenylalanine contains both a positive and a negative charge. The ammonium group (-NH3^+) is positively charged, while the carboxylate group (-COO^-) carries a negative charge. The structure can be represented as:
H
|
H2N-C-COO^-
|
CH(CH3)
|
C6H5
where the C6H5 represents the phenyl group.
Step 2
Step 3
Draw the structures of both dipeptides formed when phenylalanine reacts with serine.
Answer
The reaction between phenylalanine and serine results in two dipeptides: phenylalanine-serine and serine-phenylalanine. Their structures are:
- Phenylalanine-Serine:
H
|
H2N-C-COO^- + OH-C-CH2-COO^-
|
CH(CH3) . . . . H2
|
C6H5
- Serine-Phenylalanine:
H
|
H2N-C-COO^- + H-C-CH2
| |
CH(CH3) . . . COO^-
|
C6H5
Step 4
Name and outline a mechanism for the reaction between CH₃CH₂COCl and CH₃CH₂NH₂.
Answer
In this reaction, the mechanism is termed 'nucleophilic acyl substitution.' The steps are as follows:
-
Nucleophilic attack: The lone pair on the nitrogen of ethylamine attacks the carbonyl carbon of the acyl chloride, forming a tetrahedral intermediate.
-
Loss of leaving group: The tetrahedral intermediate collapses, leading to the expulsion of chloride ion (Cl^-).
-
Formation of amide: A proton is transferred to the oxygen, resulting in the formation of the amide bond.
The IUPAC name of the organic product is ethyl N-ethylpropanamide.